Eager for this year to end? Bad news: you'll have to wait an extra second for 2009. On December 31, the planet's official timekeepers will add a “leap second” to the coordinated universal time scale (UTC) followed around the world. The additional second makes up for the difference in two clocks – one based on Earth’s rotation and the other on the more precise atomic time of the UTC.

In the U.S., the extra second will be added by the U.S. Naval Observatory at 6:59:59 p.m. Eastern Standard Time (11:59:59 p.m. Universal time). It will be the 24th “leap second” tacked on to the universal time scale since 1972.

Universal time is based on atomic energy, with one second defined as the length of 9,192,631,770 energy transitions of the cesium atom. Before the era of atomic time, seconds were based on the speed of Earth’s rotation – but that’s been slowing by 2 milliseconds per day per century because of tidal friction.

Here's a new reason to look forward to the switch back to standard time Sunday morning: it may lower your chance of suffering a heart attack.

Heart attacks decrease by 5 percent the first Monday after the time change, and by 1.5 percent over that week, according to an analysis in this week's New England Journal of Medicine. The findings are based on 20 years of data from a Swedish registry of nine million residents.

The springtime transition to daylight saving time poses more of a health hazard: Heart attacks increase by 5 percent over the first week after clocks are pushed back an hour, spiking by 10 percent on that Tuesday, epidemiologists at the Karolinska Institute in Stockholm found.

Once upon a time, physicists raised eyebrows when they said we existed in multiple universes. But this "many worlds" theory has become widely accepted since it was first proposed in 1957 by eccentric physicist Hugh Everett.

Everett, who died in 1982 at the age of 51, is the subject of a new documentary, Parallel Worlds, Parallel Lives, which airs today at 8 P.M. Eastern time on PBS. Journalist Peter Byrne, whose 2007 profile of Everett in Scientific American explains the theory and describes Everett's troubled private and professional life, appears in the film.

"If everything physically possible happens in the universe, why do we only see one possibility at a time? That's the question philosophers are beating their heads bloody trying to answer," Byrne tells us.  "Everett's answer is there's more than one you, and you are splitting into trillions of copies of yourself every time there's a quantum interaction of a certain size."

Is a wristwatch worth more than half a million dollars? If it belonged to Albert Einstein, the answer isn't relative.

An anonymous bidder has coughed up $596,000 for a gold wristwatch worn by the physicist whose special theory of relativity proposed that time slows down or speeds up depending on how fast things are moving.

Perhaps the buyer hopes its magic will rub off; Einstein took his inspiration from concrete problems of timekeeping, Peter Galison notes in his book Einstein's Clocks, Poincare's Maps.

Einstein received the watch in 1931, as a gift from a rabbi during a luncheon of a Zionist convention at the Ambassador Hotel in Los Angeles, says Michelle Halpern, a spokeswoman for New York auctioneer Antiquorum, which sold the 81-year-old watch yesterday. Einstein emigrated to the United States two years later.